Pumped Heat Energy Storage (PHES) systems store excess power from an electrical grid during periods of excess electricity and generate electricity to upload to the electrical grid during high demand periods. Generally, PHES systems store the excess power in the form of heat or thermal energy, and subsequently generate electricity from the stored heat energy. In a PHES system, a motor may utilize electrical energy to drive a heat pump cycle. The heat pump cycle may move thermal energy from a cold reservoir to a hot reservoir to thereby store the thermal energy. When desired, a heat engine cycle may be utilized to extract and convert the stored thermal energy to produce mechanical energy, which may be utilized to generate electricity.
Operational efficiencies of the PHES system may be determined, at least in part, by a ratio of mechanical work or energy generated to the thermal energy stored. While the operational efficiencies of the PHES system may be improved by increasing the efficiencies of equipment and machines used to operate the heat pump cycle and the heat engine cycle, the equipment and machines needed to achieve the increased efficiencies are generally cost-prohibitive. For example, in a conventional PHES system, a working fluid directly contacts a stationary mass of the thermal storage media to store the thermal energy. Due to the direct contact between the stationary mass, the entire volume of the thermal storage media must be pressurized to a pressure of the working fluid. Accordingly, when the PHES system is operated at a relatively high base pressure, more robust and cost-prohibitive storage tanks must be utilized.
What is needed, then, is an improved PHES system and method for storing and generating electricity.